16 ART. 3. — T. ICHIMURA : OX THE FORMATION OF 



]3rotantliocyan into a coloured antliocyan in the red Hortense 

 seem to be : — 



a). Sunlight. — Those ealyx-leaves which are situated in the 

 shade or are overlapped by others never become red. An excep- 

 tional case of rare occurrence in which the formation of anthocyan 

 is independent of sunlight was observed by Zopf in the root of 

 Parnassia palustris. Also the red pigment which occurs in such 

 an underground organ as the sweet-potato or the red raddish 

 seems to have little need of sunlight for its formation. 



b). Acidity. — It has been generally ascertained by previous 

 observers that the red pigment can not exist without an acid 

 cell-sap in the living state. 



The crystals of calcium oxalate with the aid of intercellular 

 air-spaces may serve as a protecting medium to the delicate young 

 calyx-leaf against strong sunlight, as they reflect the light and 

 hinder a too speedy transpiration. Schimper^^ states that leaves 

 which have grown in the full sunshine are richer in crystals of 

 calcium oxalate than those grown in the shade. But the calyx- 

 leaf differs from ordinary green leaves in this respect, since these 

 crystals aje formed before chlorophyll granules appear. 



c). Tannin and sugar.- — Many observations render it probable 

 that the mother substance of anthocyan is a peculiar tannin 

 matter. The calyx-leaf of the red Hortense, however, never 

 produces red anthocyan in the absence of sunlight, though it 

 contains tannin. The root of Parietaria diffusa produces red 

 anthocyan pnly in its tannin idioblasts. Hence some plants appear 

 to require light more than tannin, and others tannin more than 

 light, for the development of anthocyan. 



]) Scliimpcr, A. F. W. — Uel)ei- Kalkoxalatliililnns in dem LauliMiiUer. (Bot. Zeitg. 

 1888, p. 8r!). 



